The invention relates to apparatus for perforating running webs of paper, plastic foil or the like. More particularly, the invention relates to improvements in perforating apparatus of the type wherein the web which is to be provided with spaced-apart transversely extending perforations is caused to pass through the nip of two rolls one of which constitutes an anvil for one or more elongated perforating tools on the other roll.
Apparatus of the just outlined character are normally provided with a timing shaft which drives the two rolls in opposite directions by way of a gear train. Such apparatus can be used with advantage for the making of coherent forms or like sheets having predetermined sizes and being readily separable from each other along the rows of perforations. The web of paper which is to be converted into a series of coherent forms is caused to pass through an imprinting mechanism before it reaches the nip of the rolls, and the thus treated web is thereupon folded back and forth in zig-zag fashion to be converted into a pile of overlapping forms wherein each intermediate form is separably connected to a pair of neighboring forms. As a rule, the length of the peripheral surface (as measured in the circumferential direction) of the roll which carries the perforating tools exceeds the length of a single form, i.e., such roll carries two or more perforating tools so that it can provide the running web with two or more transversely extending rows of perforations in response to each revolution of its shaft.
A drawback of conventional perforating apparatus is that even minor deviations of mutual distances of neighboring tools from one another, or very small differences between the perforating tools, can result in the accumulation of highly unsatisfactory stacks. For example, if one of the rolls carries two perforating tools and the mutual spacing of the tools (considered in the circumferential direction of the respective roll) deviates from ideal spacing by 0.05 mm, a first form is 0.05 mm shorter than an ideal form, the second form is 0.05 mm longer than an ideal form, the third form is 0.05 mm shorter, and so forth. If the stack has 2000 coherent forms and the thickness of a form is 0.1 mm, the height of one side of the stack exceeds the height of the opposite side by 100 mm. Such stacks must be discarded because they are unsightly and cannot be readily packed and/or otherwise treated.
In accordance with a known proposal, the aforedescribed drawbacks of conventional perforating apparatus are eliminated by starting the apparatus to form a stack, measuring the stack and providing the roll for the perforating tools with shims whose dimensions are selected with a view to ensure the formation of more satisfactory stacks if the dimensions of the measured (first) stack deviate from optimum dimensions. This is a time-consuming operation, especially since the same procedure must be repeated whenever the apparatus is to be set up for the making of longer or shorter forms.
In accordance with another known proposal, the means for rotating the roll for the perforating tools includes a gear which is mounted on an adjustable eccentric. This renders it possible to impart to the corresponding roll a slightly irregular rotary movement. The phase of such irregular movement can be changed only when the gear is at a standstill; therefore, an accurate adjustment is possible only by continuing the trial and error procedure as long as necessary. This is also a time-consuming operation which is particularly undesirable when one and the same apparatus is to be used to make shorter or longer forms.